The present invention relates to solid electrolytic capacitors using solid electrolyte and a method for manufacturing the same.
Due to the remarkable development of digital equipment in recent years, there is a strong demand for capacitors having high frequency characteristics, which are of low impedance even in a high frequency range. As capacitors available to meet such demand of the market, capacitors using solid electrolyte layers such as manganese dioxide, polypyrrole or polythiophene are known.
FIG. 3 is a sectional view showing the configuration of a conventional solid electrolytic capacitor. In FIG. 3, a dielectric oxide film 33 formed by an positive electrode oxidation method is disposed on the surface of an positive electrode body 32. The positive electrode body 32 is enclosed in the dielectric oxide film 33. The positive electrode body 32 is made by sintering valve metal such as aluminum and titanium into porous metal. Positive electrode lead wire 31 is connected to the positive electrode body 32, and a part of the positive electrode lead wire 31 is outwardly led from the surface of the dielectric oxide film 33.
A solid electrolyte layer 34 such as manganese or polypyrrole is disposed on the surface of the positive electrode body 32 having the dielectric oxide film 33, and a negative electrode layer 35 comprising a carbon layer and a conductor layer is disposed on the solid electrolyte layer 34. A capacitor element 36 is formed in this way. An positive electrode terminal 37 is connected to the positive electrode lead wire 31 of a capacitor element 36. A negative electrode terminal 39 is connected to the negative electrode layer 35 via conductive adhesive 38. Facing resin 40 being electrically insulative is disposed so as to cover the capacitor element 36. The positive electrode terminal 37 and the negative electrode terminal 39 are partially exposed to the outside. The solid electrolytic capacitor is configured in this way.
In such conventional solid electrolytic capacitor, the solid electrolyte layer 34 is extremely low in resistibility, and it has been able to reduce the equivalent series resistance (hereinafter called ESR characteristic) of the solid electrolytic capacitor.
However, in a conventional solid electrolytic capacitor as mentioned above, in case the oxide of transition metal such as manganese dioxide, or solid electrolyte layer 34 contains a conductive polymer comprising heterocyclic compound such as polypyrrole, and in a case a carbon layer is formed on the solid electrolyte layer 34 by use of aqueous solution including carbon particles and coagulation stabilizer, it will sometimes cause generation of uneven carbon layers or thin film portions because the surface tension of the aqueous solution is too high. Therefore, it has been extremely difficult to form uniform carbon layers.
Accordingly, lots of defective products have been generated with respect to ESR characteristic and capacity utilization factor, and as a result, there has been a problem of lowering in yield of the products.
The present invention provides a solid electrolytic capacitor assuring excellent ESR characteristic and capacity utilization factor, which has been reduced in contact resistance between the solid electrolyte layer and negative electrode layer, and a method for manufacturing same.
A solid electrolytic capacitor in accordance with the present invention comprises
an positive electrode body,
a dielectric layer formed on the surface of the positive electrode body,
a solid electrolyte layer formed on the surface of the dielectric layer,
a negative electrode layer disposed on the surface of the solid electrolyte layer,
an positive electrode terminal electrically connected to the positive electrode body, and
a negative electrode terminal electrically connected to the negative electrode layer,
wherein the negative electrode layer includes a carbon layer, and
the carbon layer contains carbon particles, and a benzene compound represented by chemical formula 1.
where each of R1, R2, R3, and R4 has H, OH group, COOH group, or alkyl group.
Preferably, the positive electrode body includes valve metal, and the dielectric layer includes a dielectric oxide film formed by oxidation of the valve metal.
Preferably, the negative electrode layer further includes a conductor layer, a carbon layer is disposed on the surface of the dielectric layer, and the conductor layer is disposed on the surface of the carbon layer.
Preferably, the positive electrode body includes valve metal; the dielectric layer includes a dielectric oxide film formed by oxidation of the valve metal; the negative electrode layer further includes a conductor layer; a carbon layer is disposed on the surface of the dielectric oxide film; and the conductor layer is disposed on the surface of the carbon layer.
Preferably, the solid electrolytic capacitor further comprises facing resin; each of the positive electrode terminal and the negative electrode terminal is partially exposed; and the facing resin is disposed so as to cover the positive electrode body, the dielectric layer, the solid electrolyte layer, and the negative electrode layer.
Due to this configuration, the carbon layer formed is fine and uniform. Accordingly, the contact resistance between the solid electrolyte layer and the carbon layer will be reduced. Further, the contact resistance between the carbon layer and the conductor layer will also be reduced. As a result, it is possible to obtain a solid electrolyte capacitor assuring excellent ESR characteristic and capacity utilization factor.